On Fri, 2022-07-15 at 16:51 +0800, CK Hu wrote:

Hi, Bo-Chen:

On Tue, 2022-07-12 at 19:12 +0800, Bo-Chen Chen wrote:

quoted

From: Markus Schneider-Pargmann <msp@baylibre.com>

This patch adds a embedded displayport driver for the MediaTek
mt8195
SoC.

It supports the MT8195, the embedded DisplayPort units. It offers
DisplayPort 1.4 with up to 4 lanes.

The driver creates a child device for the phy. The child device
will
never exist without the parent being active. As they are sharing a
register range, the parent passes a regmap pointer to the child so
that
both can work with the same register range. The phy driver sets
device
data that is read by the parent to get the phy device that can be
used
to control the phy properties.

This driver is based on an initial version by
Jitao shi [off-list ref]

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Guillaume Ranquet <redacted>
Signed-off-by: Bo-Chen Chen <redacted>
---

[snip]

quoted

+static void mtk_dp_hpd_sink_event(struct mtk_dp *mtk_dp)
+{
+	ssize_t ret;
+	u8 sink_count;
+	u8 link_status[DP_LINK_STATUS_SIZE] = {};
+	u32 sink_count_reg = DP_SINK_COUNT_ESI;
+	u32 link_status_reg = DP_LANE0_1_STATUS;
+
+	ret = drm_dp_dpcd_readb(&mtk_dp->aux, sink_count_reg,
&sink_count);

According to your last reply, if drm_dp_dpcd_readb() fail, we could
skip below statement. So this just for error checking? If so, the
next
drm_dp_dpcd_read() would also do the error checking, so the checking
here is redundant.

Regards,
CK

Hello CK,

sorry, I don't get your point.
We use "drm_dp_dpcd_readb(&mtk_dp->aux, sink_count_reg, &sink_count)"
to get sink count and use "drm_dp_dpcd_read(&mtk_dp->aux,
link_status_reg, link_status, sizeof(link_status));" to get link
status.

If we don't get any sink count, we don't need to check the link status.
Therefore, we just return if we are failed to get sink count.

BRs,
Bo-Chen

quoted

+	if (ret < 1) {
+		drm_err(mtk_dp->drm_dev, "Read sink count failed\n");
+		return;
+	}
+
+	drm_dbg(mtk_dp->drm_dev,
+		"read sink count from dpcd: %d\n", sink_count);
+
+	ret = drm_dp_dpcd_read(&mtk_dp->aux, link_status_reg,
link_status,
+			       sizeof(link_status));
+	if (!ret) {
+		drm_err(mtk_dp->drm_dev, "Read link status failed\n");
+		return;
+	}
+
+	if (!drm_dp_channel_eq_ok(link_status, mtk_dp-

quoted

train_info.lane_count)) {

+		drm_err(mtk_dp->drm_dev, "Channel EQ failed\n");
+		return;
+	}
+
+	if (link_status[1] & DP_REMOTE_CONTROL_COMMAND_PENDING)
+		drm_dp_dpcd_writeb(&mtk_dp->aux,
DP_DEVICE_SERVICE_IRQ_VECTOR,
+				   DP_REMOTE_CONTROL_COMMAND_PENDING);
+}
+